Probably no, but we could simplify such opcodes:
void JIT::emit_op_jtrue(Instruction* currentInstruction)
{
unsigned target = currentInstruction[2].u.operand;
emitGetVirtualRegister(currentInstruction[1].u.operand, regT0);
Jump isZero = branchPtr(Equal, regT0,
ImmPtr(JSValue::encode(jsNumber(0))));
addJump(emitJumpIfImmediateInteger(regT0), target);
addJump(branchPtr(Equal, regT0,
ImmPtr(JSValue::encode(jsBoolean(true)))), target);
addSlowCase(branchPtr(NotEqual, regT0,
ImmPtr(JSValue::encode(jsBoolean(false)))));
isZero.link(this);
RECORD_JUMP_TARGET(target);
}
The second two checks would be unnecessary, and probably we could squeeze
out a little performance gain here.
Zoltan
PS: I didn't say this is much better, instead, I would be interested in
your opinion whether you think this would be a good idea or not.
> Is there a place where testing for booleans is currently expensive?
>
> Geoff
>
> On Mar 4, 2011, at 5:37 AM, Zoltan Herczeg wrote:
>
>> Hi,
>>
>> I found something interesting in the v8 source code. They store the true
>> and false as integers: 1 and 0. Actually it was a surprise to me, but
>> "true + 1" is "2" in JavaScript, so this kind of object handling seems
>> ok.
>>
>> Advantage of their approach: they don't need to care about boolean
>> values
>> for all arithmetic and conditional operations in JIT. This could reduce
>> the source code (maintainability), and probably faster, since you don't
>> need to check boolean values.
>>
>> Disadvantage: type resolving is a bit more difficult, but since that is
>> a
>> rare operation, I think the gain could be bigger.
>>
>> What is your opinion about it? Would it be possible to implement
>> something
>> like this for JSValue32_64? Would it worth it?
>>
>> Regards,
>> Zoltan
>>
>>
>> _______________________________________________
>> squirrelfish-dev mailing list
>> [email protected]
>> http://lists.webkit.org/mailman/listinfo.cgi/squirrelfish-dev
>
>
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